This verse is hard to understand in English. In Greek it's also tricky, but the imagery is clearer: a literal translation of the first clause would be "therefore letting go of the word (Word?) of the dominion of Christ let us be borne upon perfection (ten teleioteta)..."
And verse two should be read "of baptisms, of teaching..." The appearance of the word "doctrine" in both verses 1 and 2 of the KJV makes it appear that both instances translate a single underlying word, but they don't. And I think they're a wrong insertion both times.
The imagery, though, is an exhortation to progress forward from the moment of grasping the Lord at the veil and build upon the rock. Baptism, teaching, laying on of hands, and even judgment are identified as things that do not exist within the veil.